Powder molding machine and method for filling molding materials into a die cavity thereof

ABSTRACT

A powder molding machine capable of providing a uniform density of molding powders filled in a molding cavity of a die for improving the strength of molded products includes a die, upper and lower punches and a feeder, and is further provided with a feeder driving unit, which reciprocates a feed shoe between an advanced position at which molding powder is supplied to the die and a retracted position at which no interference occurs during a pressing operation by the punches. The feed driving unit includes a mechanism for enabling the feeder shoe to pass over the die and also to be swung in left and right directions while retracting and while still over the die.

TECHNICAL FIELD

The present invention relates to the improvement of a feeder and theimprovement of a method for filling molding materials into a cavity in apowder molding machine designed to press molding powder supplied into amolding space (cavity) in a die by a punch to produce molded products.

BACKGROUND ART

A powder molding machine, as shown in FIG. 5, forcibly presses moldingpowder filled into a molding space (cavity) 3 of a die 2 by a punch(only a lower punch 14 is shown in FIG. 5), thus producing moldedproducts. A feed shoe 1 is used for filling the molding powder into theaforesaid molding space 3.

The die 2 is usually mounted on a plate 27 having a flat surface so thatthe top surface of the die becomes flush with that of the plate. Thefeed shoe 1 is linearly reciprocated in the front and rear directionwhile sliding on the aforesaid plate 27. As seen from thecross-sectional view shown in FIG. 5, the feed shoe 1, having a shapejust like that of an upside-down bowl, stores molding powder in itsinterior, and drops the molding powder stored in the interior into themolding space 3 of the die 2 as the feed shoe advances. The moldingpowder is always supplied from a hopper (not shown) located above thefeed shoe 1 through a flexible hose 36.

After the feed shoe 1 is advanced to supply the molding powder S intothe molding space 3 of the die, and is then retreated from the moldingspace 3, the surface of molding powders filled in the molding space 3 ofthe die becomes undulate. This is because portions having high densityand low density appear almost like waves in the filled powder S. This iscaused by the following reason: when the feed shoe 1 is retreated, aplurality of swirls, which rotate in a specific direction such as themoving direction of the feed shoe 1, are made in the powder filled inthe interior of the feed shoe 1, as shown in FIG. 5, and these swirlsdisturb the uniformity of density of the molding powder filled in themolding hollow space 3 of the die 2. In particular, in the case wherethe depth of molding space 3 is shallow, the powder uniformly filled iseasy to be disturbed when the feed shoe is retreated. For this reason,the density of the front-side portion of the powder S filled in themolding space 3 becomes low; on the other hand, the density of therear-side portion of the powder S becomes high.

As described above, if the powder filled in a state in which the densityis not uniform is pressed by means of a punch, the density of moldedproducts thus obtained has a non-uniform density, and its strengthlowers.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a powder moldingmachine and a method for filling molding materials into a die cavity,which is capable of making the density of molding powder filled in amolding space (cavity) of a uniform, and improving the strength of themolded products.

To achieve the above object, the present invention provides a powdermolding machine, wherein a plate and a die whose top surface is flushwith the top surface of the plate are mounted to a frame, and a feedshoe is slidable on the plate to pass over a molding space defined inthe die, thereby causing the molding materials stored in said feed shoeto be dropped into the molding space, including:

linear driving means for moving the aforesaid feed shoe in both theadvancing and retreating or retracting directions with respect to theaforesaid molding space defined in the die from its retreat position;

swing driving means for swinging the said feed shoe in a directiongenerally traverse to the advancing and retreating directions; and

a mechanism for giving the feed shoe a motion in a direction broughtabout by the combination of the aforesaid linear driving means and swingdriving means when both means are driven.

Preferably, said swing driving means is fixed to a frame of the powdermolding machine to rotate a casing supporting the feed shoe at apredetermined angle with respect to the frame, and the linear drivingmeans is fixed to the casing to enable the feed shoe to project orretract from the casing.

More preferably, the powder molding machine further includes one or twoor more position detecting means for detecting an arbitrary positionbetween the retreat or retracted position and the most advanced positionof the feed shoe, and transmission means for transmitting an outputdetected by the position detecting means to both or any one of saidlinear driving means and swing driving means.

In addition, the present invention provides a method for filling moldingmaterials in a die cavity of a powder molding machine, comprising thesteps of:

dropping molding materials stored in a feed shoe into a die cavity bymoving the feed shoe over the die cavity from a retreat position; and

swinging said feed shoe, when said feed shoe is retreating from theposition of said die cavity to its retreat position, in transversedirections with respect to its retreating direction as long as at leasta part of said feed shoe overlaps said cavity.

As described above, according to the present invention, the feed shoepasses over the cavity, during which powder is in the cavity, whilebeing swung in the left and right directions when retreating, so thatthe uniformity of density of molding powders filled in the cavity willnot be adversely affected by retreating motion of the feed shoe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional front view of a mechanism of a feed shoeaccording to the present invention;

FIG. 2 is a top plan view of the associated mechanism of the feed shoeshown in FIG. 1;

FIG. 3 is a partial sectional front view of the entirety of the powdermolding machine;

FIG. 4 is a view illustrating a retreating operation of the feed shoeaccording to the present invention;

FIG. 5 is a cross-sectional view showing a state in which moldingpowders are supplied to the feed shoe by a conventional method;

FIG. 6 is a graph illustrating density distribution when moldingmaterials are filled in the cavity by the conventional method;

FIG. 7 is a schematic view showing an appearance of powder when moldingmaterials are filled in the cavity by the conventional method;

FIG. 8 is a graph illustrating density distribution when moldingmaterials are filled in the cavity by the method according to thepresent invention; and

FIG. 9 is a schematic view showing an appearance of powder when moldingmaterials are filled in the cavity by the method according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A powder molding machine 4 has the configuration in which a moldingdevice 6 and a feeder 7 are mounted on a frame 5 having an upper wall 9,an intermediate wall 10 and a lower wall 11, as shown in FIG. 3, and adrive of the machine is controlled by means of a NC unit 8.

A ball-bearing nut 16 is rotatably installed in the upper wall 9 of theframe 5, and engages with a ball-bearing screw 12 for driving an upperpunch 13. A ball-bearing nut 18 is rotatably installed in the upper wall9 of the frame 5, and engages with a ball-bearing screw 15 for driving alower punch 14. In addition, the center of each of these ball-bearingscrews 12 and 15 is aligned with an axis a extending in the up-and-downdirection shown in FIG. 3.

A die mounting portion 26 with step, which has an opening penetrating inthe up-and-down direction, and is coaxial with the aforesaid axis a, isformed in the intermediate wall 10 of the frame 5. The die 2 is mountedon the die mounting portion 26, and is fixed on the intermediate wall 10by means of the plate 27. The top surface of the die 2 thus mounted isaligned with the top surface of the plate 27. The open space penetratingin the up-and-down direction is constituted so that the upper punch 13attached to the distal end of the ball-bearing screw for driving theupper punch, and the lower punch 14 attached to the distal end of theball-bearing screw 15 for driving the lower punch, are inserted into thespace from above and below, respectively.

The ball-bearing nut 16 mounted on the upper wall 9 of the frame 5 isrotated by means of a drive of a servo motor 17 mounted on the upperwall 9 through a driving pulley 21 fixed on an output shaft of the servomotor 17, and a timing belt 22 wound around a driven pulley 20 fixed onthe ball-bearing nut 16 and the aforesaid driving pulley 21. Theball-bearing nut 18 mounted on the lower wall 11 of the frame 5 isrotated by means of a drive of a servo motor 19 mounted on the lowerwall 11 through a driving pulley 24 fixed on an output shaft of theservo motor 19, and a timing belt 25 wound around a driven pulley 23fixed on the ball-bearing nut 18 and the aforesaid driving pulley 24.

When the upper and lower ball-bearing nuts 16 and 18 are rotated bymeans of the drive Of servo motors 17 and 19, respectively, theball-bearing screws 12 and 15 for driving the upper and lower punchesare moved up and down along the aforesaid axis a, thereby the upper andlower punches 13 and 14 being moved in a space of the die 2.

The molding device 6 comprises the upper and lower ball-bearing nuts 16and 18, ball-bearing screws 12 and 15 for driving the upper and lowerpunches, upper and lower punches 13 and 14, and servo motors 17 and 19for driving these ball-bearing nuts.

The NC unit 8 executes general operational sequence control of themolding powder machine, and molding program control according toinputted programs and data. A load cell 29 is installed in the lowerball-bearing nut 18 to detect the actual pressing force of upper the andlower punches which is applied to the molding powder supplied into thespace of the die. The detected output data is fed back to the NC unit 8.

A hopper 30 for temporarily storing powdered molding materials ismounted on the upper wall 9 of the frame 5. A feeder 7 for filling themolding materials into the die cavity is installed in the intermediatewall 10. The details of the feeder 7 will be explained later.

In FIG. 3, the reference numeral 46 denotes an ejecting unit forejecting molded products by an action of a solenoid, and the referencenumeral 47 denotes a chute for receiving the molded products ejected bythe aforesaid ejecting unit 46 from the lower punch 14.

The powder molding machine 4 described above with reference to FIG. 3has a construction similar to that disclosed in Japanese PatentLaid-open Publication No. Hei 1-181997, for example.

In an embodiment according to the present invention, the aforesaidfeeder 7 is characterized by including a feed shoe 1, which is mountedon the distal end of an arm 31, a motor 32 for linear motion, whichgives advance/retreat motion to the aforesaid feed shoe 1, and a motor33 for swinging motion, which gives left and right swinging motion tothe aforesaid feed shoe 1, as shown in FIGS. 1 and 2. The details of theconfiguration will be described below.

A pivot 35 stands erect at the top surface of intermediate wall 10 ofthe frame 5, and a casing 34 is rotatably supported by means of thepivot 35, as shown in FIGS. 1 and 2.

The feed shoe 1 has a shape like an upside-down bowl similar to aconventional feed shoe, and its interior is defined so that moldingpowder can be stored therein. The molding powder is supplied to theinterior of the feed shoe 1 through a flexible hose 36 connecting thefeed shoe 1 with a hopper 30. A base end of the arm 31 is fixed to oneside of the feed shoe 1.

The arm 31, which has a rack gear 43 formed on one side of the arm 31over almost the entire length thereof, is inserted into the aforesaidcasing 34. A notch is formed at one place on the side of the casing 34so that the rack gear 43 of the arm 31 inserted in the casing 34 isexposed. The motor 32 for linear motion is installed on the top surfaceof the casing 34 in the vicinity of the portion where the aforesaidnotch is formed so that an output shaft 44 of the motor is directeddownward. A pinion gear 38, which is fixed to the distal end of theoutput shaft 44, engages with the rack gear 43 of the arm 31 inserted inthe casing 34 through the aforesaid notch. Therefore, when the motor forlinear motion is rotated in the normal or reverse direction, the arm 31is projected or retracted from the casing 34.

A gate-shaped mounting base 37 for installing the motor 33 for swingingmotion is mounted on the top surface of the intermediate wall 10 of theframe 5 so that it extends over the rear portion of the casing. Themotor 33 for swinging motion is installed on the aforesaid mounting base37 so that an output shaft 45 of the motor is directed downward. Aneccentric cam 39 fixed to the distal end of the output shaft 45 isarranged so as to abut on a side face of the casing 34. The position atwhich the casing 34 abuts on the eccentric cam 39 is a short distanceaway from the pivot 35 rotatably supporting the casing 34 towards thereverse side of the feed-shoe side. Therefore, when the motor 33 forswinging motion is driven with respect to the casing 34 supported by thepivot 35, the casing 34 is pressed by rotation of the eccentric cam 39,and is swung at a predetermined angle with the pivot 35 being thecentral axis. An attracting spring 41, whose respective ends are fixedto the casing 34 and the intermediate wall 10, respectively, is used foralways keeping the side face of the casing 34 in contact with theeccentric cam 39.

A molding operation of a powder molding machine according to anembodiment of the present invention will be described below.

Upper and lower punches 13 and 14, which are selected in accordance witha desired molded product, are respectively attached to the distal end ofthe ball-bearing screw 12 (for driving the upper punch) and to that ofthe ball-bearing screw 15 (for driving the lower punch). The die 2corresponding to these upper and lower punches 13 and 14 is fitted intothe die mounting portion 26 of the intermediate wall 10 of the frame 5,and is fixed so that the top surface of the die is flush with the topsurface of the plate 27.

Also, the upper punch 13 is situated at the retreat position above andaway from the die 2 before the powder molding machine is operated. Onthe other hand, the lower punch 14 is situated in a predeterminedposition located in the die space 28 penetrating through the center ofthe die 2, from below, thus defining the molding space 3 (cavity) by thedie 2 and the lower punch 14. The feed shoe 1 of the feeder 7 issituated at the retreat position (shown by the broken line in FIG. 4)away from the die 2, and molding powder is supplied to the interior ofthe feed shoe from the hopper 30 through the flexible hose 36. Theeccentric cam 39 is situated at the neutral position, that is, the arm31 is in a state in which it is not inclined towards either left orright direction.

If an operation starting command is given to the NC unit 8 in theaforesaid state, the NC unit 8 controls the drive by each of servomotors 17 and 19 of the powder molding machine 4, the motor 32 forlinear motion, and the motor 33 for swinging motion according to thespecified machining programs and various data previously inputted.

When the operation starting command is given to the NC unit 8 in thestate as described above, the motor 32 for linear motion is first drivenin the normal direction. Then, the arm 31 fixing the feed shoe 1 ismoved forward with respect to the casing 34 by engagement of the piniongear 38 attached to the distal end of the output shaft 44 of the motor32 for linear motion with the rack gear 43 formed in the arm 31. Inother words, the feed shoe 1 is moved so that it advances toward themolding space 3 from the initial retreat or retracted position.

During advancing motion of the feed shoe 1, the motor 33 for swingingmotion is not driven, so that the advancing motion of the feed shoe 1becomes motion along a straight line. The casing 34 is kept in a statein which it is inclined to neither a left nor a right direction by theelastic force of the spring 41 and the contact with the eccentric cam39.

Further, when the feed shoe 1 is moved on the plate 27 until reachingthe overhead position of the molding space 3 defined by the die 2 andthe lower punch 14, the molding powder stored in the interior of thefeed shoe 1 is dropped into the molding space 3, thereby filling themolding space 3 with the molding powder.

Next, when the motor 32 for linear motion is driven in thereverse-rotational direction, the arm 31 is retreated or retracted. Inother words, the feed shoe 1 is moved to the initial retreat positionfrom the overhead position of the molding space 3. During retreatingmotion of the feed shoe 1, the motor 33 for swinging motion is driven.Therefore, when the eccentric cam 39 attached to the distal end of theoutput shaft 45 of the motor 33 for swinging motion is rotated, thecasing 34 with the retreating arm 31 retracted thereinto is swung inleft and right directions at a predetermined angle against elastic forceof the spring 41.

When the feed shoe 1 passes through the overhead position of the moldingspace 3 filled with the molding powder while retreating, the feed shoe 1is moved while swinging in the left and right direction, as indicated bya moving locus of an arbitrary point in the feed shoe 1 shown in a topplan view of FIG. 4. Thus, the density of the molding powder in thespace 3 of the die is prevented from being uneven.

The motor 33 for swinging motion is driven as long as the retreatingfeed shoe 1 overlaps even partially with the molding space 3. Theposition where the drive of the motor 33 for swinging motion is stoppedmay be set by locating a limit switch (not shown) in a predeterminedposition, or may be the same as the position where the motor 33 forlinear motion is stopped. It is necessary, however, for the motor 33 forswinging motion to be set to stop at the point at which the eccentriccam 39 comes to rest at its neutral position.

When the feed shoe 1 reaches the initial retreat position, the motor 32for linear motion is stopped. The position where the feed shoe 1 isstopped is set by locating a limit switch (not shown) at a predeterminedposition in the intermediate wall 10 of the frame 5. In this case, aposition where the feed shoe 1 does not interfere with a subsequentpunch pressing operation is selected as the aforesaid stop position ofthe feed shoe.

After that, the powder filled in the molding space undergoes acompression molding operation according to the ordinary method. Morespecifically, when the servo motor 17 for driving the upper punch isrotated in the normal direction, the upper ball-bearing nut 16 isrotated through the driving pulley 21, timing belt 22, and driven pulley20. Then, the ball-bearing screw 12 for driving the upper punch iscaused to come down by the rotation of the upper ball-bearing nut 16, bywhich the upper punch 13 attached to the distal end of the ball-bearingscrew 12 is inserted into the molding space 3 to press the moldingpowder filled in the molding space 3. The servo motor 19 for driving thelower punch is simultaneously driven in the normal direction, by whichthe lower ball-bearing nut 18 is rotated through the driving pulley 24,timing belt 25, and driven pulley 23 to cause the ball-bearing screw 15for driving the lower punch to be lifted.

In this manner, the molding powder filled in the molding space 3 ispressed from above and below by means of the upper and lower punches 13and 14. Therefore, a large pressing force can be provided, and theportion where the density of the pressed powder is relatively low can beset to the middle portion in the up-and-down direction. However, in thecase where there is no need of a large pressing force, such as when amolded product with a small thickness is required, or the like, thepressing operation described above may be carried out by only thedescending linear motion of the ball-bearing screw 12 for driving theupper punch under the condition that the servo motor 19 for driving thelower punch is locked by means of a solenoid brake or the like.

A pressing force generated by descending linear motion of theball-bearing screw 12 for driving the upper punch, or by the combinationof descending linear motion of the ball-bearing screw 12 for driving theupper punch and ascending linear motion of the ball-bearing screw 15 fordriving the lower punch, is detected by means of the load cell 29mounted on the lower ball-bearing nut 18, and is inputted to the NC unit8 as a feedback signal.

The NC unit 8 controls the command supplied to the servo motors 17 and19 on the basis of the aforesaid feedback signal, and keeps the pressingforce at a preset value. When a preset time has elapsed, the servomotors 17 and 19 for driving the upper and lower punches will bestopped, thereby releasing the molded product from the pressing forceapplied. Then, the servo motor 19 for driving the lower punch is drivenin the reverse direction, while the servo motor 17 for driving the upperpunch is driven in the normal direction. Descending motion of theball-bearing screw 15 for driving the lower punch and that of theball-bearing screw 12 for driving the upper punch take place at equalspeeds. This will cause the upper and lower punches 13 and 14 to comedown through the die space 28 in a state in which the interval betweenthe both is kept constant, whereby the molded product is taken out ofthe die 2 in a state in which it is laid on the top surface of the lowerpunch 14.

When the molded product is taken out of the die 2, the servo motor 19for driving the lower punch is stopped, while the servo motor 17 fordriving the upper punch is driven in the reverse direction.Simultaneously, the molded product ejecting unit 46 is driven to ejectthe molded product laid on the lower punch 14 into the chute 42, therebyenabling the molded product to be taken out of the powder moldingmachine 4. Further, the servo motor 17 for driving the upper punch isdriven in the reverse direction and a drive of the servo motor 19 fordriving the lower punch is driven in the normal direction, whereby theupper and lower punches 13 and 14 are returned to the aforesaid initialposition to complete one cycle of the molding operation.

As described above, in the present embodiment, to obtain theconstruction in which the feed shoe is moved to the overhead position ofthe die cavity from the retreat position, and the feed shoe is retreatedtoward the aforesaid retreat position while being swung in left andright directions as it is moved toward the aforesaid retreat position,two motors 32 and 33 are used as components for the above construction,which function as linear driving means and swing driving means, casing34, eccentric cam 39, arm 31 with a rack, and the like. However, all ofthe operations of the feed shoe which take place on the plate 27 may bereplaced by a robotic operation.

Concerning the filling of the specific molding material, explained inthe following is an example of a comparative test in which the result offilling in the case (A) where the feed shoe is first advanced straightfor filling and then retreated straight and the result of the filling inthe case (B) where the feed shoe is advanced straight and retreatedwhile being swung towards lift and right directions.

In this test, a water-atomized iron powder (apparent density of 2.93Mg.m⁻³) was mixed with lead stearate of 1% by weight as a lubricant bymeans of a rolling mill for half an hour to prepare a mixture (withapparent density of 3.24 Mg.m⁻³ and particle size of 70 to 100 μm) foruse in the test. A die cavity to be filled with the powder was of squareshape with equal sides of 70 mm (with corner R of 5 mm) and depth of 1mm. A linear speed in the directions of advancing and retreating of thefeed shoe was set to 150 mm/sec. In addition, a swinging motion of thefeed shoe for obtaining the result of filling in the case (B) wasperformed for every 5 mm of retreating motion, with 18 mm of amplitudeof that swinging motion set.

FIGS. 6 and 8 are bar graphs showing average density at each of ninedifferent portions (3 times 3 equals 9) in the powder filled into thecavity in the cases of (A) and (B). Comparing these bar graphs, it canbe seen that dispersion of filling density in the cavity in the fillingresult of case (B) was less than that,of the filling result of case (A).In addition, the general average of the density of the filled powder inthe case (B) was higher than that of the filled powder in the case (A).

FIGS. 7 and 9 schematically show the appearance of each of pressedpowders representing the filled results of case (A) and case (B). Asseen from FIG. 7, the portion located at the level about 2/3 in thecavity viewed from the advancing direction of the feed shoe is blank,indicating that the blank portion is a poorly filled portion. On theother hand, in FIG. 9, when observed carefully, a striped pattern causedby the swinging operation of the feed shoe can be recognized, but theblank portion, as shown in FIG. 7 does not appear therein. This meansthat filling has been done evenly.

As is obvious from this test, a better filling result can be obtained inthe case where the feed shoe is retreated while being swung after it islinearly advanced to fill the molding materials in the cavity than inthe case where the feed shoe is linearly retreated after it is linearlyadvanced to fill the molding materials in the cavity.

What is claimed is:
 1. A powder molding machine, comprising:a frame; a plate mounted on said frame and having a top surface; a die having a top surface flush with the top surface of said plate, said die having a molding cavity defined therein; a feed shoe slidable along the top surface of said plate and having a space therein for holding molding materials, said molding materials dropping into said molding cavity when said feed shoe passes over said molding cavity; linear driving means for moving said feed shoe in a linear direction from a retracted position to a position over said molding cavity and for retracting said feed shoe back to said retracted position; swing driving means for driving said feed shoe in a non-circular motion by swinging said feed shoe in directions traverse to said linear direction and cooperating with said linear driving means for swinging said feed shoe during retraction to said retracted position; and control means for causing simultaneous operation of said linear driving means and said swing driving means while said shoe overlaps any part of said molding cavity and is being retracted to said retracted position to create a combination of retracting said linear and swinging transverse motions of said shoe to uniformly distribute said molding materials throughout said molding space.
 2. A powder molding machine according to claim 1, further comprising:a casing rotatably attached to said frame, said shoe being operatively connected to an inner end of said casing; andwherein said linear driving means and said swing driving means are connected to said casing to cause said linear and swinging transverse motions of said shoe.
 3. A powder molding machine according to claim 2, wherein said linear driving means includes a rack and pinion mechanism.
 4. A powder molding machine according to claim 2, wherein said swing driving means includes cam means in contact with said casing to cause swinging movement of said shoe.
 5. A powder molding machine according to claim 1, further comprising:position detecting means for detecting a predetermined position between the most retracted position and the most advanced position of said feed shoe; and transmitting means for transmitting an output detected by said position detecting means to at least one of said linear driving means and said swing driving means.
 6. A method for filing molding materials in a die cavity of a powder molding machine, comprising the steps of:dropping molding materials stored in a feed shoe into a die cavity by advancing said feed shoe to a position over said die cavity from a retracted position; and driving said feed shoe in a non-circular motion, as said feed shoe is retracted from the position over said die cavity to its retracted position, in transverse directions to its retracting direction as long as at least a part of said feed shoe overlaps said cavity.
 7. A powder molding machine, comprising:a frame; a plate mounted on said frame and having a top surface; a die having a top surface flush with the top surface of said plate, said die having a molding cavity defined therein; a feed shoe slidable along the top surface of said plate and defining a space to hold molding materials, said molding materials dropping into the molding cavity when said feed shoe passes over said molding cavity; a motor to linearly move said feed shoe between a retracted position and a position over said molding cavity; and a rack and pinion mechanism to swing said feed shoe in a non-circular motion traverse to said linear movement during retraction of said feed shoe. 